Electroluminescence device

ABSTRACT

An organic EL element has excellent features as compared with other electroluminescent elements, but on the other hand, has a problem that the life of the element is not sufficiently long. In addition, since the organic EL element is expected to be applied to a mobile display and the like, it is also important to improve power efficiency. Hence, an object of the invention is to provide an element structure to realize an improvement in power efficiency and an improvement in the life of the element at the same. In the construction of an organic EL element of the invention, the first electroluminescent film  303  is sandwiched by the first anode  302  and a cathode  304 , and the second electroluminescent film  305  and the second anode  306  are laminated over the cathode  304 . At this time, the first anode  302  is put into contact with the second anode  306  to form a parallel circuit to decrease an electric current passing through the respective electroluminescent films.

This application is a continuation of U.S. application Ser. No.10/763,101 filed Jan. 22, 2004 now U.S. Pat. No. 7,199,521.

FIELD OF THE INVENTION

The present invention relates to an electroluminescence device with ananode, a cathode and a layer comprising an organic compound that emitslight by applying an electrical voltage.

BACKGROUND OF THE INVENTION

Compared to inorganic compounds, organic compounds include more variedmaterial systems, and through appropriate molecular design it ispossible to synthesize organic materials having various functionalities.Further, the organic compound is characterized in that films and thelike formed using the organic compound demonstrate great pliancy, andsuperior process ability can also be achieved by polymerization. Inlight of these advantages, in recent years, attention has been given tophotonics and electronics employing functional organic materials.

Photonic techniques which make use of photophysical qualities of organiccompounds have already played an important role in contemporaryindustrial techniques. For example, photosensitive materials, such as aphotoresist, have become indispensable in a photolithography technologyused for fine processing of semiconductors. In addition, since theorganic compounds themselves have properties of light absorption andconcomitant light emission (fluorescence or phosphorescence), they haveconsiderable applicability as light emitting materials such as laserpigments and the like.

On the other hand, since organic compounds do not have carriersthemselves, they essentially have superior insulation properties.Therefore, in the field of electronics where the electrical propertiesof organic materials are utilized, the main conventional use of organiccompounds is insulators, where organic compounds are used as insulatingmaterials, protective materials and covering materials.

However, there are means for making massive amounts of electricalcurrent flow in the organic materials which is essentially insulators,and they are starting to be put to practical use in the electronicsfield. The means discussed here can be broadly divided into twocategories.

The first of these, represented by conductive polymers, is means inwhich a π-conjugate system organic compound is doped with an acceptor(electron acceptor) or a donor (electron donor) to give the π-conjugatesystem organic compound a carrier “Synthesis of Electrically ConductingOrganic Polymers: Halogen Derivatives of Polyacetyrene, (CH)_(x))” byHideki Shirakawa et al., Chemical Communications, 1977, 16, 578-580. Byincreasing the doping amount, the carrier will increase up to a certainarea. Therefore, its dark conductivity will also increase together withthis, so that significant electricity will be made to flow.

Since the amount of the electrical flow can reach the level of a normalsemiconductor or more, a group of materials which exhibit this behaviorcan be referred to as organic semiconductors (or, in some cases, organicconductors).

This means of doping the acceptor/donor to improve the dark conductivityto make the electrical current flow in the organic material is alreadybeing applied in part of the electronics field. Examples thereof includea rechargeable storage battery using polyaniline or polyacene and anelectric field condenser using polypyrrole.

The other means for making massive electrical current flow in theorganic material uses an SCLC (Space Charge Limited Current). The SCLCis an electrical current which is made to flow by injecting a spacecharge from the outside and moving it, the current density of which isexpressed by Child's Law, i.e., Formula (1), shown below. In theformula, J denotes a current density, ∈ denotes a relative dielectricconstant, ∈₀ denotes a vacuum dielectric constant, μ denotes a carriermobility, V denotes a voltage, and d denotes a distance (hereinafter,referred to as “thickness”) between electrodes applied with the voltageV:

[Formula 1]J=9/8·∈∈₀ μ·V ² /d ³  (1)

Note that the SCLC is expressed by Formula (1) in which no carrier trapwhen the SCLC flows is assumed at all. The electric current limited bythe carrier trap is referred to as a TCLC (Trap Charge Limited Current),and it is proportionate to a power of the voltage, but both the SCLC andthe TCLC are currents that are subject to bulk limitations. Therefore,both the SCLC and the TCLC are dealt with in the same way hereinbelow.

Here, for comparison, Formula (2) is shown as a formula expressing thecurrent density when an Ohm current flows according to Ohm's Law. σdenotes a conductivity, and E denotes an electric field strength:

[Formula 2]J=σE=σ·V/d  (2)

In Formula (2), since the conductivity σ is expressed as σ=neμ (where ndenotes a carrier density, and e denotes an electric charge), thecarrier density is included in the factors governing the amount of theelectrical current that flows. Therefore, in an organic material havinga certain degree of carrier mobility, as long as the material's carrierdensity is not increased by doping as described above, the Ohm currentwill not flow in a material which normally does not have few carriers.

However, as is seen in Formula (1), the factors which determine the SCLCare the dielectric constant, the carrier mobility, the voltage, and thethickness. The carrier density is irrelevant. In other words, even inthe case of an organic material insulator with no carrier, by making thethickness d sufficiently small, and by selecting a material with asignificant carrier mobility μ, it becomes possible to inject a carrierfrom the outside to make the current flow.

Even when this means is used, the current flow amount can reach thelevel of a normal semiconductor or more. Thus, an organic material witha great carrier mobility μ, in other words, an organic material capableof latently transporting a carrier, can be called an organicsemiconductor.

Incidentally, even among organic semiconductor elements which use theSCLC as described above, organic electroluminescent elements(hereinafter, referred to as “organic EL elements”) which use both thephotonic and electrical qualities of functional organic material asphotoelectronic devices, have particularly demonstrated remarkableadvancement in recent years.

The most basic structure of the organic EL element was in year of 1987.“Organic Electroluminescent Diodes” by C. W. Tan et al., Applied PhysicsLetters, Vol. 51, No. 12, 913-915 (1987). The element reported inNon-patent document 2 is a type of diode element in which electrodessandwich an organic thin film having a total thickness of approximately100 nm and being constituted by laminating a hole-transporting organiccompound and an electron-transporting organic compound, and the elementuses a light emitting material (fluorescent material) as theelectron-transporting compound. By applying voltage to the element,light-emission can be achieved like a light emitting diode.

The light-emission mechanism is considered to work as follows. That is,by applying the voltage to the organic thin film sandwiched by theelectrodes, the hole and the electron injected from the electrodes arerecombined inside the organic thin film to form an excited molecule(hereinafter, referred to as a “molecular exciton”), and light isemitted when this molecular exciton returns to its base state.

Note that, types of molecular excitons formed by the organic compoundcan include a singlet excited state and a triplet excited state, and thebase state is normally the singlet state. Therefore, emitted light fromthe singlet excited state is referred to as fluorescent light, and theemitted light from the triplet excited state is referred to asphosphorescent light. The discussion in this specification covers casesof contribution to the emitted light from both of the excited states.

In the case of the organic EL element described above, the organic thinfilm is normally formed as a thin film having a thickness of about 100to 200 nm. Further, since the organic EL element is a self-luminouselement in which light is emitted from the organic thin film itself,there is no need for such a back light as used in a conventional liquidcrystal display. Therefore, the organic EL element has a great advantagein that it can be manufactured to be extremely thin and lightweight.

Further, in the thin film having a thickness of about 100 to 200 nm, forexample, the time from when the carrier is injected to when therecombination occurs is approximately several tens of nanoseconds, giventhe carrier mobility exhibited by the organic thin film. Even when thetime required by for the process form the recombination of the carrierto the emission of the light, it is less than an order of microsecondsbefore the light emission. Therefore, one characteristic of the organicthin film is that response time thereof is extremely fast.

Because of the above-mentioned properties of thinness andlightweightness, the quick response time, and the like, the organic ELelement is receiving attention as a next generation flat panel displayelement. Further, since it is self-luminous and its visible range isbroad, its visibility is relatively good and it is considered effectiveas an element used in display screens of portable devices.

The organic EL element has excellent features described above, on theother hand, the reason why it is not yet widely put into actual use is adrawback that the life of the element is not sufficiently long.

In an electroluminescent film constructing the organic EL element, thedeterioration of function of its organic semiconductor is accelerated bythe passage of electric current. It is known that in the organic ELelement, the life of the element (half-life of luminescent luminance)deteriorates in a manner nearly inversely proportional to initialluminance, in other words, inversely proportional to the amount ofelectric current to be passed. The Japan Society of Applied Physics,Journal of Molecular Electronics and Bioelectronics, Vol. 11, No.1(2000), 86-99.

From this fact, it can be said that to decrease the amount of electriccurrent passing through the electroluminescent film of the organic ELelement is important not only from the viewpoint of power consumptionbut also from the viewpoint of the life of the element.

Therefore, an object of the invention is to provide an element structurethat reduces the amount of electric current passing through theelectroluminescent film of an organic EL element to improve the life ofthe element.

SUMMARY OF THE INVENTION

The invention is a electroluminescence device that includes: the firstelectrode formed on a substrate; the first electroluminescent film incontact with the first electrode; the second electrode in contact withthe first electroluminescent film; the second electroluminescent film incontact with the second electrode; and the third electrode in contactwith the second electroluminescent film, and is characterized in thatthe first electrode and the third electrode function as one of an anodeor a cathode and in that the second electrode function as the other ofthe anode or the cathode.

Here, the first electrode and the third electrode may be electricallyconnected to each other.

Further, the invention is an electroluminescence device having anotherconstruction characterized in that a plurality of anodes and a pluralityof cathodes are alternately formed over a substrate and in thatelectroluminescent films are formed between the respective anodes andcathodes.

In the electroluminescence device, the plurality of anodes may beelectrically connected to each other and the plurality of cathodes maybe electrically connected to each other.

Further, in the electroluminescence device, light can be taken out froma substrate side by preventing only the electrode farthest from thesubstrate, of the electrode selected from any of the anodes andcathodes, from transmitting light.

Still further, in the electroluminescence device, light can be alsotaken out from the opposite side of the substrate by preventing only theelectrode closest to the substrate, of the electrode selected from anyof the anodes and the cathodes, from transmitting light.

Still further, in the electroluminescence device, light can be alsotaken out from both of the substrate side and the opposite side of thesubstrate by making all of the anodes and the cathodes included in thelight emitting element transmissive.

In this regard, in the electroluminescence device, two or more kinds ofelectroluminescent elements each of which emits different light can beused for the plurality of electroluminescent elements.

In addition, in the electroluminescence device, white light can be alsoemitted by using at least one electroluminescent element of emitting redlight, at least one electroluminescent element of emitting green light,and at least one electroluminescent element of emitting blue light asthe plurality of electroluminescent elements.

In this regard, the electroluminescence device in this specificationmeans an image display device or an electroluminescence device using anelectroluminescent element having an electroluminescent film as anelectroluminescent element. Moreover, the electroluminescence deviceincludes all of a module in which a electroluminescent element ismounted with a connector, for example, an anisotropic conductive film(ACF) or a tape automated bonding (TAB) tape or a tape carrier package(TCP), a module in which a printed wiring board is mounted on the tip ofa TAB tape or a TCP, and a module in which a electroluminescent elementis directly mounted with an integrated circuit (IC) by a chip on glass(COG) method.

The invention is characterized in that power efficiency per unit areacan be improved by connecting the electroluminescent films in parallelto the electrodes and by laminating them vertically. In addition, thelife of the element can be improved by decreasing the amount of electriccurrent supplied to the electroluminescent films.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration to show the fundamental construction of theinvention.

FIG. 2 is an illustration to show the fundamental construction of theinvention.

FIG. 3 is an illustration to show the minimum construction of thefundamental construction of the invention.

FIG. 4 is an illustration to show the state where electrons and holesflow in the minimum construction of the invention.

FIGS. 5(A) and 5(B) are illustrations to show the comparison between theinvention and a prior art.

FIGS. 6(A) and 6(B) are illustrations to show an electroluminescencedevice of an active matrix structure.

FIG. 7 is a detail illustration of an electroluminescent film(embodiment 2).

FIG. 8 is a detail illustration of an electroluminescent film(embodiment 3).

FIGS. 9(A), 9(B) and 9(C) are illustrations to show the direction inwhich light is emitted.

FIGS. 10(A) to 10(G) show applications of an electroluminescence device.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(Mode 1)

FIG. 1 and FIG. 2 are schematic views of the invention. In FIG. 1,anodes and cathodes that are connected to the same external electrodeare provided on a substrate 101 alternately in the order closer to thesubstrate as follows: the first anode 102, the first cathode 104, thesecond anode 106, the second cathode 108, . . . , the n-th cathode 109,and the (n+1)-th anode 111. The first electroluminescent film 103 isformed between the first anode 102 and the first cathode 104; the secondelectroluminescent film 105 is formed between the first cathode 104 andthe second anode 106; the third electroluminescent film 107 is formedbetween the second anode 106 and the second cathode 108; and the 2n-thelectroluminescent film 110 is formed between the n-th cathode 109 andthe (n+1)th anode 111, and one electroluminescent element is formed bythe electroluminescent film sandwiched between a pair of the anode andthe cathode. FIG. 2 is an example in which electrodes are laminated on asubstrate 201 in such an order as a cathode 202, an anode 204, a cathode206, . . . , an anode 209, and a cathode 211, and in whichelectroluminescent films 203, 205, 207, 210 are formed between theelectrodes, respectively. FIG. 2 is identical to FIG. 1 except that onlythe order of lamination of the electrodes is different.

Further, in FIG. 1 and FIG. 2, when the lamination of the electrodes onthe substrate starts with the anode, it ends with the anode and when thelamination of the electrodes on the substrate starts with the cathode,it ends with the cathode. However, needless to say, even if thelamination of the electrodes starts with the anode, it may end with thecathode, and vice versa. It is recommendable to set the number of anodesand cathodes to be laminated at a suitable one as required.

Further, a substance excellent in hole injection is suitable for eachanode and a substance having a large work function (about 4.5 to 5.5 eV)is preferably used for the anode. The substance includes, for example,Ti, TiN, TiSi_(X)N_(Y), Ni, W, WSi_(X), WN_(X), WSi_(X)N_(Y), NbN, Mo,Cr, Pt, Se, Pd, Ir, and Au, and a mixture or an alloy of these. It issaid that a substance excellent in hole injection and having a smallwork function (about 2.5 to 3.5 eV) (typically, a metal elementbelonging to the 1st group or the 2nd group of the periodic table) or analloy containing these substances is preferably used for the cathode.Among them, alloys such as MgAg, MgIn, and AlLi are desirable as thematerial used for the cathode.

(Mode 2)

The fundamental principle of the invention will be described on thebasis of the structure shown in FIG. 3, which is a minimum constructionin the invention. Here, a word of “transmissive” means “transparent”, or“in a state sufficient for transmitting light”.

FIG. 3 is an example in which the first anode 302, the firstelectroluminescent film 303, a cathode 304, the secondelectroluminescent film 305, the second anode 306 are formed over thetransmissive substrate 301. Transmissive electrodes are used for thefirst anode 302, the cathode 304, and the second anode 306.

The state of flow of electrons and holes in a case where electriccurrent is flowed through an element of the structure shown in FIG. 3 isshown in FIG. 4. The holes are injected from two anodes as shown by areference numeral 401 in the drawing, and the electrons are injectedinto both of the upper and lower electroluminescent films from thecenter cathode as shown by a reference numeral 402. At this time, whenan electric current of I is supplied from an external power source asshown by an arrow 501 in FIG. 5(B), an electric current of I/2 flowsthrough each of the first anode and the second anode, as shown by anarrow 502 and then an electric current of I/2 flows through each of thefirst electroluminescent film and the second electroluminescent film.Assuming that the number of photons emitted when an electric current ofI flows through one electroluminescent film is N, N/2 photons areemitted from each of the electroluminescent films, as shown by an arrow503 and the total number of photons emitted from two electroluminescentfilms becomes N.

On the other hand, in a case where an electric current of I is flowedthrough an element of a structure, shown in FIG. 5(A), of sandwichingone electroluminescent film by an node and a cathode from an externalpower source, as shown by an arrow 501, N photons are emitted from theelectroluminescent film, as is the case with FIG. 5(B).

Comparing FIG. 5(A) with FIG. 5(B), when a same number of photons areemitted, the amount of electric current supplied from the external powersource is I in both cases, but in the case of using the structure shownin FIG. 5(B), the amount of electric current that is required to flowthrough one electroluminescent film is as little as I/2, which can hencereduce the deterioration of the electroluminescent film caused by theelectric current.

Further, let's think about power consumption. Assuming that in theelement having the structure shown in FIG. 5(A), the electric currentrequired to emit N photons from the electroluminescent film is I andthat a voltage required to flow the current of I is V, the powerconsumption P_(a) of the element of this structure is as follows.

[Mathematical formula 3]P _(a) =I·V  (3)

In contrast to this, in the element shown in FIG. 5(B), the totalelectric current required to emit a total of N photons from twoelectroluminescent films is I but since a circuit is a parallel circuit,it is clear from the mathematical formula (1) that a voltage required tobe supplied from the external power source is V/√2. Here, the electricpower P_(b) required to emit N photons by the element shown in FIG. 5(B)is shown as follows.

[Mathematical formula 4]P _(b) =I/2×V/√2×2=I×V/√2  (4)

In this manner, in the case of using the structure disclosed in theinvention, electric power required to emit a same number of photons canbe decreased by a factor of 1/√2 as compared with an element of astructure commonly used.

To realize the structure shown in FIG. 3, it is important to connect theanode 302 to the anode 306 without shorting of the anode 302 and thecathode 304 and without shorting of the cathode 304 and the anode 306.As for means for this purpose, selective coating by the use of a metalmask is suitably used.

While only a case where the number of the electroluminescent films istwo has been described above, the invention can be also applied to astructure including three or more electroluminescent films shown inFIG. 1. Further, similarly, the invention can be also applied to thestructure shown in FIG. 2.

Embodiment 1

In this embodiment, first, an electroluminescence device having anelectroluminescent film of the invention in a pixel part will bedescribed by the use of FIGS. 6(A) and 6(B). Here, FIG. 6(A) is a topview to show an electroluminescence device and FIG. 6(B) is a sectionalview taken on a line B-B′ in FIG. 6(A). A part 601, a part 602, and apart 603, each shown by a dotted line, are a drive circuit part (sourceside drive circuit), a pixel part, and a drive circuit part (gate sidedrive circuit), respectively. Further, a reference numeral 604 denotes asealing substrate and 605 denotes a sealing agent, and an inside portion607 surrounded by the seal agent 605 is a hollow space.

Here, a reference numeral 608 denotes a wiring for transmitting a signalto be input to the source side drive circuit 601 and the gate side drivecircuit 603 and receives a video signal, a clock signal, a start signal,a reset signal, and the like from a FPC (flexible printed circuit) 609that is an external input terminal. In this regard, only FPC is shownhere but this FPC may be mounted with a printed wiring board (PWB). Itis assumed that the electroluminescence device in this specificationincludes not only an electroluminescence device proper but also anelectroluminescence device mounted with a FPC or a PWB.

Next, a sectional structure will be described by the use of FIG. 6(B).While the drive circuit part and the pixel part are formed over asubstrate 610, the source side drive circuit 601 that is a drive circuitpart and the pixel part 602 are shown here.

In this regard, a CMOS circuit of a combination of an n-channel type TFT623 and a p-channel type TFT 624 is formed as the source side drivecircuit 601. Further, the drive circuit may be formed of a PMOS circuitor an NMOS circuit. Still further, while a driver-integrated type inwhich a drive circuit is formed on a substrate is shown in thisembodiment, a driver is not necessarily to be formed on a substrate butcan be formed outside.

Further, the pixel part 602 is formed of a plurality of pixels includinga TFT 611 for switching, a TFT 612 for electric current control, and thefirst anode 613 electrically connected to its drain. An insulator 614 isformed in such a manner as to cover the end of the first anode 613.Here, the insulator 614 is formed by the use of a positive acrylic resinfilm.

Still further, to improve a covering ratio, a curved surface having acurvature is formed on the top end portion or the bottom end portion ofthe insulator 614. For example, in the case of using a positivephotosensitive acrylic resin as the material of the insulator 614, it ispreferable that only the top end portion of the insulator 614 has acurved surface having a radius of curvature (from 0.2 μm to 3 μm).Moreover, both of a negative material that is made insoluble in enchantby photosensitive light and a positive material that is made soluble inenchant by the light can be used.

In this regard, the insulator 614 needs to have an anode contact 621 forconnecting the first anode 613 to the second anode 619.

The first electroluminescent film 616, the first cathode 617, the secondelectroluminescent film 618 and the second anode 619 are formed on thefirst anode 613, respectively.

Here, it is desirable that a material having a large work function isused as a material used for the first anode 613 and the second anode619. For example, not only a single layer film such as an ITO (indiumtin oxide) film, an indium zinc oxide (IZO) film, a titanium nitridefilm, a chromium film, a tungsten film, a Zn film, and a Pt film, butalso a laminated layer of a titanium nitride film and a film containingaluminum as a main component and a three-layer structure of atitaniumnitride film, a film containing aluminum as a main component,and a titanium nitride film can be used.

Here, since at least one of the first anode 613 and the second anode 619needs to be transparent enough to transmit light, a metal thin film thatis thin enough to transmit light is used, or a transparent conductivefilm is used, or a laminated layer of a metal thin film and atransparent conductive film is used.

Further, the first electroluminescent film 616 and the secondelectroluminescent film 618 are formed by a vapor deposition methodusing a vapor-deposited mask or an ink jet method. As for a materialused for an electroluminescent layer, a single layer or a laminatedlayer of an organic compound is used in many cases, but the inventionincludes a construction in which an inorganic compound is used for aportion of a film made of an organic compound.

Still further, it is recommended that a material having a small workfunction (Al, Ag, Li, or Ca, or an alloy of these elements MgAg, MgIn,AlLi, CaF₂, or CaN) be used as a material used for the first cathode 617held between the first electroluminescent film 616 and the secondelectroluminescent film 618.

In this respect, to transmit light generated by the firstelectroluminescent film 616 and the second electroluminescent film 618through the first cathode 617, it is recommended that a metal thin filmhaving a thin film thickness, a transparent conductive film (ITO (alloyof indiumoxide and tin oxide alloy), an alloy of indium oxide and zincoxide (In₂O₃—ZnO), zinc oxide (ZnO), and the like), or a laminated layerof the metal thin film and the transparent conductive film be used.

In addition, by bonding a sealing substrate 604 to an element substrate610 with a sealing agent 605, there is provided a structure in which theelectroluminescent element 618 is provided in a space 607 surrounded bythe element substrate 610, the sealing substrate 604, and the sealingagent 605. Here, the space 607 includes also a construction in which thespace 607 is filled with inert gas (nitrogen, argon, and the like) orthe sealing a gent 605.

In this regard, it is preferable that an epoxy base resin is used as thesealing agent 605. Further, it is desirable that these materials areones that do not transmit moisture and oxygen to the extent possible.Still further, as a material used for the sealing substrate 604 can beused not only a glass substrate and quartz substrate but also a plasticsubstrate made of FRP (fiberglass-reinforced plastics), PVF (polyvinylfluoride), Mylar, polyester, acrylic, or the like.

In this manner, the electroluminescence device having anelectroluminescent element of the invention can be produced.

Embodiment 2

In this embodiment will be described the structure of anelectroluminescent element in a case where an anode is used for anelectrode at a position closest to a substrate.

The structure of a structure laminated on the first anode 613 will bedescribed in detail. Here, an electroluminescent film and the firstcathode 617 are manufactured by the vapor deposition method and a metalthin film that is thin enough to transmit light is used for the firstcathode 617 and a transparent conductive film manufactured by thesputtering method is used for the second anode 619, and all these arepatterned and manufactured by the use of a metal mask.

In FIG. 7 is shown the detailed structure of an electroluminescentelement 620 in FIGS. 6(A) and 6(B). A hole injection layer 702, a holetransport layer 703, a electroluminescent layer 704, an electrontransport layer 705, and an electron injection layer 706 are selectivelyformed over the first anode 613 by the use of the metal mask and are notformed over an anode contact part 621. Further, the metal mask is usedproperly so as to prevent the anode from becoming shorted with thecathode.

First, a film is formed of copper phthalocyanine (hereinafter shown byCu-Pc) of a hole-injecting organic compound in a film thickness of 20 nmover the first anode 701 by the vapor deposition method to make the holeinjection layer 702. Then, a film made of 4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (hereinafter shown by α-NPD)which is a hole-transporting organic compound is formed in a filmthickness of 40 nm to make the hole transport layer 703.

Next, a film is formed of tris(8-quinolinolate) aluminum (hereinaftershown by Alq₃) of an electron-transporting electroluminescent organiccompound in a film thickness of 37.5 nm over the hole transport layer703 by the vapor deposition method to make the electroluminescent layer704. Then, similarly, a film is formed of Alq₃ in a film thickness of37.5 nm over the electroluminescent layer 704 to make the electrontransport layer 705. The electroluminescent layer 704 and the electrontransport layer 705 can be formed successively.

Further, to improve electron injection performance from the cathode, afilm made of calcium fluoride (hereinafter shown by CaF₂) of aninorganic compound is formed in a film thickness of 1 nm to make theelectron injection layer 706.

In this manner, the first electroluminescent film 709 can be obtained.

Further, a film of aluminum (hereinafter shown by Al) is formed as thefirst cathode 707 in a film thickness of 5 nm.

Thereafter, a film of CaF₂ is formed as an electron injection layer 706in a film thickness of 1 nm over the first cathode 707, a film of Alq₃is formed as an electron transport layer 705 in a film thickness of 37.5nm, a film of Alq₃ is formed as a electroluminescent layer 704 in a filmthickness of 37.5 nm, a film of α-NPD is formed as a hole transportlayer 703 in a film thickness of 40 nm, and a film of Cu-Pc is formed asa hole injection layer 702 in a film thickness of 20 nm. In this manner,the second electroluminescent film 710 can be obtained.

Further, the second anode 708 is formed by the sputtering method. Atthis time, the second anode 708 is connected to the first anode 613through the anode contact part 621 shown in FIG. 6(B) and a metal maskis used to prevent the second anode 708 from becoming shorted with thefirst cathode 617 to control the portions where the films are formed.

In this manner, the electroluminescent element 620 is completed. Here,light emitted from the electroluminescent element is emitted from bothof a substrate side and a reverse side, as shown in FIG. 9(A), becauseall electrodes are transmissive.

Embodiment 3

In this embodiment will be described the structure of anelectroluminescent element in a case where a cathode is used for anelectrode at a position closest to a substrate.

The structure of an electroluminescent element in a case where a cathodeis used for an electrode at a position closest to a substrate and therelationship between the electroluminescent element and the electrodeare shown in FIG. 8 and a reference numeral 801 in the drawing denotesthe first cathode, 807 denotes the first anode, and 808 denotes thesecond cathode. Here, details of the respective layers constructing therespective electroluminescent films are the same as those in theabove-described embodiment 2 and are denoted by the same referencenumerals.

The element shown in this embodiment shows the same action as theelement of the above-described embodiment 2.

Embodiment 4

In this embodiment will be described a structure in which light isemitted only from the opposite side of the substrate, as shown in FIG.9(B).

As shown in the above-described embodiment 3, an anode at a positionclosest to the substrate is made a cathode. However, the first cathode907 is formed of Al as in a film thickness of 200 nm so as not totransmit light.

The structure except for the first cathode 907 can be the same as theabove-described embodiment 2. Then, of light emitted from theelectroluminescent layer, light emitted to the substrate side isreflected by the first cathode 907, as shown by an arrow 905, and hencelight is emitted only from the opposite side of the substrate, as shownby an arrow 906 shown in FIG. 9(B).

In this manner, the structure in which light is emitted only from theopposite side of the substrate can be realized.

Embodiment 5

In this embodiment will be described a structure in which light isemitted only from a substrate side, as shown in FIG. 9(C).

As shown in the above-described embodiment 3, an anode at a positionclosest to the substrate is made a cathode. However, as shown in FIG.9(C) a cathode 910 at a position farthest from the substrate is formedof Al in a film thickness of 200 nm so as not to transmit light.

The structure except for the first cathode can be the same as theabove-described embodiment 2. Then, of light emitted from theelectroluminescent layer, light emitted from the opposite side of thesubstrate is reflected by the cathode 910 of a thick film as shown by anarrow 908 and hence light is emitted only from the substrate side, asshown by an arrow 909 shown in FIG. 9(C).

In this manner, the structure in which light is emitted only from thesubstrate side can be realized.

Embodiment 6

In this embodiment will be described an electroluminescence device ofemitting white light by the use of two electroluminescent elements eachof which emits light of different color.

The construction of this embodiment is the same as that of theabove-described embodiment 2 except for an electroluminescent layer.

In this embodiment, two electroluminescent layers are constructed of anelectroluminescent element to emit blue light and an electroluminescentelement to emit orange light which is in a relationship of complementarycolor to the blue light. Here, the relationship of complementary colormeans two different colors that can produce white light when lights ofthe two different colors are mixed with each other.

Since two electroluminescent layers are controlled by one power sourcesystem, both the electroluminescent layers emit at the same time torealize the emission of white light.

Embodiment 7

In this embodiment will be described an electroluminescence device ofemitting white light by the use of three kinds of electroluminescentelements each of which emits different color.

A structure shown in this embodiment is a structure including threeelectroluminescent elements. This structure corresponds to a structurein a case where there are three electroluminescent elements sandwichedbetween the anode and the cathode in FIG. 1 and FIG. 2.

The structure of this embodiment is the same as that in embodiment 2except for the electroluminescent layer.

In the structure including the above-described three electroluminescentelements, three electroluminescent elements each of which emitsdifferent color, including an electroluminescent element of emitting redlight, an electroluminescent element of emitting green light, and anelectroluminescent element of emitting blue light are used for the threeelectroluminescent layers, respectively.

Since these three electroluminescent elements are controlled by onepower source system, they emit light at the same time to realize theemission of white light.

Embodiment 8

In this embodiment will be described various kinds of electricappliances completed by the use of an electroluminescence device havingan electroluminescent element of the invention.

The electric appliances manufactured by the use of a electroluminescencedevice having an electroluminescent element of the invention include avideo camera, a digital camera, a goggle type display (head-mounteddisplay), a navigation system, an audio reproduction device (car audiodevice, audio component, and the like), a notebook personal computer, agame machine, a portable information terminal (mobile computer, mobiletelephone, mobile game machine, electronic book, and the like), an imagereproduction device provided with a recording medium (to be specific, adevice of reproducing the recording medium such as digital video disk(DVD) and the like and provided with a display device capable ofdisplaying a reproduced image), and the like. The embodiments of theseconcrete electric appliances are shown in FIG. 11.

FIG. 10(A) shows a display device that includes a case 1001, a supportbase 1002, a display part 1003, a speaker part 1004, a video inputterminal 1005 and the like. This display device is manufactured by usingan electroluminescence device having an electroluminescent element ofthe invention for the display part 1003. Here, the display deviceincludes all devices for displaying information such as for personalcomputer, for the reception of TV broadcasting, and for the display ofadvertisement.

FIG. 10(B) shows a notebook personal computer that includes a main body1101, a case 1102, a display part 1103, a keyboard 1104, an externalconnection port 1105, a pointing mouse 1106, and the like. This notebookpersonal computer is manufactured by using an electroluminescence devicehaving an electroluminescent element of the invention for the displaypart 1103.

FIG. 10(C) shows a mobile computer that includes a main body 1201, adisplay part 1202, a switch 1203, an operating key 1204, an infrared rayport 1205, and the like. This mobile computer is manufactured by usingan electroluminescence device having an electroluminescent element ofthe invention for the display part 1202.

FIG. 10(D) shows a mobile image reproduction device provided with arecording medium (to be specific, a DVD reproduction device) thatincludes a main body 1301, a case 1302, a display part A 1303, a displaypart B 1304, a recording medium (DVD and the like) reading part 1305, anoperating key 1306, a speaker part 1307, and the like. The display partA 1303 displays mainly image information and the display part B displaysmainly character information. This mobile image reproduction device ismanufactured by using electroluminescence devices each having anelectroluminescent element of the invention for these display parts A1303 and B 1304. Here, the image reproduction device provided with arecording medium includes a game machine intended for home use and thelike.

FIG. 10(E) shows a goggle type display (head-mounted display) thatincludes a main body 1401, a display part 1402, and an arm part 1403.This goggle type display is manufactured by using an electroluminescencedevice having an electroluminescent element of the invention for thedisplay part 1402.

FIG. 10(F) shows a video camera that includes a main body 1501, adisplay part 1502, a case 1503, an external connection port 1504, aremote control reception part 1505, an image reception part 1506, abattery 1507, a voice input part 1508, an operating key 1509, an eyecontact part 1510, and the like. This video camera is manufactured byusing an electroluminescence device having an electroluminescent elementof the invention for the display part 1502.

Here, FIG. 10(G) shows a mobile telephone that includes a main body1601, a case 1602, a display part 1603, a voice input part 1604, a voiceoutput part 1605, an operating key 1606, an external connection port1607, an antenna 1608, and the like. This mobile telephone ismanufactured by using an electroluminescence device having anelectroluminescent element of the invention for the display part 1603.Here, the power consumption of the mobile telephone can be reduced bydisplaying white characters against a black background in the displaypart 1603.

As described above, the scope of application of the electroluminescencedevice having an electroluminescent element of the invention isextremely wide and this electroluminescence device can be applied toelectric appliances in all fields.

1. A mobile telephone comprising a display part, the display part havingan electroluminescence display device, the electroluminescence displaydevice comprising: a first electrode formed over a substrate; a firstelectroluminescent film in contact with the first electrode; a secondelectrode in contact with the first electroluminescent film; a secondelectroluminescent film in contact with the second electrode; and atransparent third electrode in contact with the secondelectroluminescent film, wherein an electric current flow directionthrough the first electroluminescent film is different from an electriccurrent flow direction through the second electroluminescent film. 2.The mobile telephone according to claim 1, wherein the number of thedisplay part is one.
 3. The mobile telephone according to claim 1,wherein electrodes comprising the first electrode and the thirdelectrode function as one of an anode or a cathode and the secondelectrode functions as the other of the anode or the cathode.
 4. Themobile telephone according to claim 1, wherein the electroluminescencedisplay is an active matrix electroluminescence display.
 5. The mobiletelephone according to claim 1, wherein the first and third electrodesare electrically connected to each other.
 6. The mobile telephoneaccording to claim 1, wherein the third electrode covers both sides ofthe second electroluminescence film.
 7. An electroluminescence displaydevice comprising: a first electrode formed over a substrate; a firstelectroluminescent film in contact with the first electrode; a secondelectrode in contact with the first electroluminescent film; a secondelectroluminescent film in contact with the second electrode; and atransparent third electrode in contact with the secondelectroluminescent film, wherein each of the first and secondelectroluminescent films comprises a hole injection layer, a holetransport layer, a electroluminescent layer, an electron transportlayer, and an electron injection layer, and wherein an electric currentflow direction through the first electroluminescent film is differentfrom an electric current flow direction through the secondelectroluminescent film.
 8. The active matrix electroluminescencedisplay device according to claim 7, wherein electrodes comprising thefirst electrode and the third electrode function as one of an anode or acathode and the second electrode functions as the other of the anode orthe cathode.
 9. The electroluminescence display according to claim 7,wherein the electroluminescence display is an active matrixelectroluminescence display.
 10. The electroluminescence displayaccording to claim 7, wherein the first and third electrodes arcelectrically connected to each other.
 11. The electroluminescencedisplay according to claim 7, wherein the third electrode covers bothsides of the second electroluminescence film.
 12. A mobile telephonecomprising a display part, the display part having anelectroluminescence display device, the electroluminescence displaydevice comprising: a first anode formed over a substrate; a firstelectroluminescent film in contact with the first anode; a cathode incontact with the first electroluminescent film; a secondelectroluminescent film in contact with the cathode; and a transparentsecond anode in contact with the second electroluminescent film, whereineach of the first and second electroluminescent films comprises a holeinjection layer, a hole transport layer, a electroluminescent layer, anelectron transport layer, and an electron injection layer, and whereinan electric current flow direction through the first electroluminescentfilm is different from an electric current flow direction through thesecond electroluminescent film.
 13. The mobile telephone according toclaim 12, wherein the number of the display part is one.
 14. The mobiletelephone according to claim 12, wherein electrodes comprising the firstelectrode and the third electrode function as one of an anode or acathode and the second electrode functions as the other of the anode orthe cathode.
 15. The mobile telephone according to claim 12, wherein theelectroluminescence display is an active matrix electroluminescencedisplay.
 16. The mobile telephone according to claim 12, wherein thefirst anode and the transparent second anode are electrically connectedto each other.
 17. The mobile telephone according to claim 12, whereinthe second anode covers both sides of the second electroluminescencefilm.